This invention relates to servo heads in disk file data storage systems. In particular, the present invention relates to an improved passive noise cancellation in the servo heads by the use of multiple servo transducers.
Disk file data storage systems contain magnetic media disks on which data is stored in concentric tracks by means of data heads which write and read magnetically encoded data. These data heads are mechanically linked to a servo head located on an electromechanical actuator. The servo head and the actuator are part of a negative feedback, closed loop servo system which is used to move the data heads (and the servo head) from one track to another for track seek operations and to hold them directly over a track for track following.
The normal output signal of the servo head is encoded radial position information, which it reads from the servo disk. However, the servo head is also susceptible of picking up external electromagnetic radiation. The main source of this external electromagnetic radiation is the data head located across from the servo head. When that data head is writing data, it is also radiating noise to the servo head. The noise corrupts the normal radial position information for the servo system, thus, reducing the track following precision. Consequently, the data written at that time may not be completely within the actual data track boundaries. Later, when this data is being read, the normal track following precision has returned. However, the data head is then flying within the track boundaries trying to read data which may not be written completely within the track boundaries. This increases the probability that data errors will occur during reading.
A passive noise cancellation technique for servo heads is described in a commonly-assigned, co-pending patent application entitled Cross Talk Cancellation for Magnetic Read Head by L. A. Wilcox, Ser. No. 159,878, filed Feb. 24, 1988, and which is hereby incorporated by reference. In this co-pending application, the servo head includes two servo transducers. The first servo transducer reads the servo information stored on the servo disk. The second servo transducer is located on the same slider as the first servo transducer, but has its pole tips recessed slightly from the servo disk surface to prevent it from reading a signal from the servo disk. The second servo transducer is connected to the first servo transducer with opposite coil polarity in either a series-opposing or parallel-opposing configuration. The noise induced in the second servo transducer (which is generated by the adjacent data head when it is writing data) tends to cancel similar noise which is induced in the first servo transducer. Therefore, during normal operation, the net output voltage of this combined servo head, even in the presence of noise, is the signal read from the servo disk by the first servo transducer.